Another way of thinking about extensions and organizing them coherently is provided by using a common or group of closely related upper structures (e.g. the first triad inversion of each major minor diminished chord) over a slash bass note. This is the sort of late romantic/ impressionist approach which is now synonymous with a lot of modern jazz music created in what might be called a post-Bill Evans/Herbie Hancock style.


A number of liberating creative options result from this kind of thinking.

If you so wish you can of course create a pool of compatible voicings to directly substitute for normal 7th and extended/ altered chords in a progression.

Alternatively harmonizing the melody using the same or similar upper structure triad creates the bonding agent tying the progression together rather than the resolution of individual chord tones. (See Ron Miller - Modal Jazz vol -advance music 1992)

Rather than as alternatives for distinct 7th or extended chords choosing the appropriate slash bass note becomes as much a matter of controlling and/or manipulating the contrapuntal relationship of the bass with the melody. (again check out Ron Miller)

The bass note can also be treated (on the basis of the overtone series) as a potential major triad and as such a countervailing key centre to that implied by the upper triad. This creates a logical basis for exploring exotic polytonal extended voicing within a framework of a cadential song form. (David Liebman - A Chromatic Approach To Jazz Harmony and Melody)

Songs can become dislocated from a central key centre. Improvising on each of the harmonies (depending on harmonic rhythm) can be difficult in the manner of a Giant Steps type progression but on the other hand yield original and stimulating results using motivic cell chains. (Check out guitarist John Abercrombie on Kenny wheeler's lovely MaBelle Helene for a clear example).

HTH

Alan